1. Field of the Invention
The present invention relates to a signal processing device, an image pickup device and a signal processing method, and in particular, a signal processing device, an image pickup device and a signal processing method that detect shake of the body of the image pickup device for obtaining image data of photographed image during photographing.
2. Description of the Related Art
Devices such as digital video cameras, digital cameras and film cameras, having a function of correcting blurring of the photographed image due to shaking of the hand holding the device body (hereinafter refer to as camera shake) during photographing have been known. In such devices, to acquire image data without image blurring even when shaking occurs due to camera shake, a shake signal corresponding to the shake is obtained by detecting shake of the device due to camera shake. As a method of detecting the shake, a sensor for detecting acceleration, angular acceleration, angular speed and the like is used and a shake signal is obtained by an output signal of the sensor.
It is known that the above-nentioned output signal of the sensor includes components other than the signal due to shake, and therefore, when the output of the sensor is used as it is, the obtained shake signal may contain error. The components other than the shake signal due to shake includes DC components such as bias voltage in the case of no input to the sensor due to shake and offset voltage representing bias voltage when power is applied. For this reason, a highpass filter is connected to the sensor so as to remove the DC component, which is the component other than the shake signal component from the output signal of the sensor. Further, to correct shake applied to the device due to camera shake (frequency of about 1 to 10 Hz), a time constant of the highpass filter is increased. However, since the output signal attenuates by intervention of the highpass filter, when many DC components are included as in the completion of panning, the output signal attenuates in the negative direction from a central value among the signal output range capable of being outputted from the sensor and then gets closer to the central value. The central value means an output signal of the sensor when the device is in a stable state. Assuming that the signal attenuated in the negative direction from the central value (hereinafter referred to as residual DC component) is not a signal corresponding to the actual shake but a shake signal that is a signal including the residual DC components, there is a possibility that detection accuracy of actual shake of the device can be lowered. For this reason, processing for removing the residual DC components has been performed, however, there is a problem that the processing takes a long time.
Therefore, the art of making time constant of the highpass filter variable is known (Refer to, for example, Japanese Patent Application Laid-pen (JP-A) No. 8-82823, pages 7 to 8 and FIG. 8, and JP-A No. 2000-187258, pages 15 to 16 and FIG. 6).
According to this technique, when power is applied or when panning is carried out, time constant is decreased. Therefore, the output signal, in which many DC components are included when panning is completed, attenuates in the negative direction and then gets closer to the central value at shorter time than in the case where time constant is large. Accordingly, it is possible to shorten the time that is necessary for removing the residual DC components.
However, according to the above-nentioned technique, although the time for removing the residual DC components can be shortened by switching time constant of the highpass filter, influence of the residual DC components cannot be controlled. Moreover, the technique requires detection of operations such as panning, whereby further configuration for switching the time constant depending on the detected result is necessary.